It is known in the field of data processing to provide an accumulator to generate a sum of multiple input values. However a particular difficulty which arises with respect to the configuration of such an accumulator for floating-point values is that in most implementations floating-point addition is non-associative, i.e. the result of adding three or more numbers depends on the order in which the additions are performed. This is due to the fact that the large range of the floating-point number encoding makes it almost inevitable that there will be loss of precision and that this loss will be different depending on the order the values are summed.
Such non-deterministic outcomes for calculations are typically rather undesirable in the context of a data processing apparatus and therefore it is known to seek to avoid them by, say, limiting the precision of the output sum such that any variations are hidden below the precision of the output sum to achieve an exact final sum or imposing constraints on the order in which the floating-point values may be summed.